The Colorado Civil Rights Commission responded to the couple’s complaint with a ruling saying the shop could not lawfully deny service to customers based on their sexual orientation. The commission said Masterpiece Cakeshop violated the Colorado Anti-Discrimination Act.

The amicus brief filed this week sides with the Colorado Civil Rights Commission.

“This Court should not establish a precedent inviting discrimination against historically marginalized communities, including but not limited to the lesbian, gay, bisexual, transgender and queer (LGBTQ) community,” the brief submitted to the Supreme Court says.

Joining in signing the brief were Colorado U.S. lawmakers Sen. Michael Bennet and Reps. Diana DeGette, Ed Perlmutter and Jared Polis. They were among 211 members of Congress who filed the brief.

An amicus brief, also known as a friend-of-the-court brief, refers to a court filing from someone who is not a party to a case offering information intended to help judges make a decision.

In the Masterpiece Cakeshop case, the decision is likely to determine whether state and federal laws can require merchants to serve all peaceable customers.

Phillips, along with the Trump administration’s Justice Department, argues that he has constitutional rights to free speech and religious liberty that allow him to deny service to some customers he disfavors.

The amicus brief from members of Congress this week said a decision for Phillips would violate the Civil Rights Act of 1964 and the Americans with Disabilities Act.

“The Court’s interpretation and application of the Colorado Anti-Discrimination Act will decide whether commercial enterprises that do business with the public have a constitutional right to discriminate,” the brief says. “The Court’s decision will therefore have significant implications for federal civil rights laws with public accommodation provisions .…”

The dispute started in July 2012 when Charlie Craig and David Mullins wanted a cake to celebrate their wedding with family and friends.

The two men, who were Colorado residents, were married in Massachusetts, which allowed same-sex marriages in 2012. Colorado law began recognizing same-sex marriages in 2014.

Craig and Mullins returned home for the marriage celebration. They received a cake from a different Denver-area bakery after Phillips refused to serve them.

Nevertheless, they filed a complaint with the Colorado Civil Rights Commission under a state law that forbids businesses open to the public from discriminating against customers based on race, religion, gender or sexual orientation. The complaint led to a lawsuit, which Craig and Mullins won.

The trial court ordered Masterpiece Cakeshop to “change its company policies, provide comprehensive staff training regarding public accommodations discrimination and provide quarterly reports for the next two years regarding steps it has taken to come into compliance and whether it has turned away any prospective customers.”

Phillips refused to comply with the court order and ceased his wedding cake business. He appealed with legal assistance from the conservative Christian advocacy group Alliance Defending Freedom.

The American Civil Liberties Union represented Craig and Mullins, eventually winning again before the Colorado Supreme Court. The state supreme court ruled that regardless of whether making a cake was an artistic expression that required individual discretion, it was part of the expected conduct for Masterpiece Cakeshop’s business.

As a result, Phillips could not deny service as an expression of his First Amendment rights to free speech and freedom of religion.

Since the appeal reached the U.S. Supreme Court last year, it has attracted dozens of amicus briefs.

The brief filed this week by 36 senators and 175 House members has won support from the gay rights advocacy group One Colorado as well as the Human Rights Campaign, the NAACP Legal Defense Fund, the National Center for Lesbian Rights and others.

“In signing this brief, we are sending a clear signal that every American – regardless of race, color, sexual orientation, or gender – should be guaranteed freedom from discrimination in all aspects of their lives,” Bennet said in a statement.